To date five ULBP/RAET (UL16-binding protein, also known as retinoic acid early transcript) genes, encoded on human chromosome 6q24.2-q25.3, have been shown to encode ligands of the activating immunoreceptor NKG2D. Here, we show that a sixth gene, ULBP6/RAET1L, is a polymorphic locus that expresses a functional transcript. ULBP6 had a more restricted expression profile in cell lines and primary human tissues than other NKG2D ligands, but expression was detected in several human papillomavirus-positive cervical carcinoma cell lines and was inducible on infection with human CMV. ULBP6 bound to recombinant NKG2D as well as the human CMV immune evasion molecule UL16. By confocal microscopy we show that UL16 retains ULBP6 inside the cell, preventing it from reaching the cell surface. Expression of ULBP6 on target cells induced a significant increase in NK-cell killing. Comparison of ULBP6 with ULBP4 and ULBP5 indicated that differences in recombinant NKG2D binding correlated with differences in NK-cell activation.Key words: Immune evasion . Infectious diseases . Innate immunity . NK cells . NK-cell ligandsSupporting Information available online IntroductionThe stimulatory immune receptor NKG2D (NK group 2, member D) plays an important role in anti-pathogen and anti-cancer immune responses [1]. In humans, NKG2D is expressed by all NK cells and almost all abT cells and gdT cells [1]. It is normally absent from CD4 1 T cells but can be induced in some circumstances, such as in rheumatoid arthritis patients [2] and on exposure to human CMV (HCMV) [3]. NKG2D signalling function is mediated exclusively through the adaptor molecule DAP10 in humans [4], whereas mouse NKG2D can associate with both DAP10 and DAP12 [5,6]. The downstream effects of NKG2D ligation are now recognised to depend on synergy with other cell surface receptors and cytokines, with IL-15 signalling recently being shown to have a particularly close association with the NKG2D-DAP10 complex [7,8].NKG2D ligands are a diverse array of cellular proteins, all of which have structural similarity to MHC class I molecules [9]. In humans NKG2D ligands are encoded in two gene families, MIC (MHC-class-I-polypeptide related sequence) and ULBP/RAET (UL16-binding protein, also known as retinoic acid early transcript) [10][11][12][13]. We will follow the ULBP nomenclature from this point. In mouse, NKG2D ligands comprise three members of the H60 family, five members of the Rae1 (retinoic acid early inducible transcript-1) family, and Mult-1 (murine ULBP-like transcript) [14][15][16][17].According to the initial models of NKG2D function, its ligands were thought to be largely absent from healthy cells, but their expression could be induced on viral infection and on tumourigenesis [1]. Ectopic expression of NKG2D ligand leads to anticancer immune responses to transplanted tumours in mice, and the NKG2D knockout mouse has an increased susceptibility to certain types of cancer [18][19][20]. The importance of NKG2D in antiviral immune responses is illustrated by the fact that ...

An effective host immune response to mycobacterial infection must control pathogen dissemination without inducing immunopathology. Constitutive overexpression of mycobacterial heat shock protein (myHsp70) is associated with impaired bacterial persistence, but the immune-mediated mechanisms are unknown. We found that myHsp70, in addition to enhancing antigen delivery to human dendritic cells, signaled through the CCR5 chemokine receptor, promoting dendritic cell aggregation, immune synapse formation between dendritic cells and T cells, and the generation of effector immune responses. Thus, CCR5 acts as a pattern-recognition receptor for myHsp70, which may have implications for both the pathophysiology of tuberculosis and the use of myHsps in tumor-directed immunotherapy.